Kelly Clarkson had mushrooms before inauguration performance

Giant dinner before Monday's ceremony

Kelly Clarkson was on mushrooms when she sang "My Country, 'Tis of Thee" at President Obama's second inauguration ceremony — stuffed mushrooms, that is.

The secret to Kelly Clarkson's seemingly effortless high notes? Carbs. Lots of carbs.

The American Idol alumnus pulled off an amazing rendition of "My Country, 'Tis of Thee" at President Barack Obama's second inauguration ceremony on Monday, and TMZ reports that she was well-fed before she sang.

Clarkson and friends dined at D.C.'s Buca di Beppo before the show. No word if that included fiancé Brandon Blackstock, though Blackstock was with Clarkson at the Inaugural ball — Clarkson tweeted a picture of the two of them dressed up for the party.

Clarkson joked that her Oscar de la Renta dress was so voluminous that she could barely cram herself into her vehicle — she displayed a photo of herself sitting with her floral dress poofed all around her.

But before the show, it was mountains of Italian food for Clarkson and friends: The group dined on lasagna, bruschetta, stuffed mushrooms, giant meatballs, chicken parmesan and spaghetti, topping the whole thing off with a colossal brownie sundae. The bill for all the food came to $230.

Sources told TMZ that Clarkson was friendly to Buca di Beppo's staff, taking time out for a few candid photos with the waiters and cooks.